Previously we wrote about a house that we built in Belgium. This house had double outside log walls (2 x 8 centimeter massive wood) with 20 centimeters cellullose between the walls.
The advantage of this construction was the damp-open construction (no plastic foils anywhere in the walls) plus the enormous thermal capacity of the walls. In the evening the walls warm the house, during summer daytime they cool the house.
And there is yet another advantage of cellulose: the fire rating. If impregnated with fire retardant material, cellulose will not burn. Look at the video below where different insulation materials are compared. It is not a scientific test, but it gives a good impression of what happens in case of fire.
We try to avoid polyethylenes and polystyrenes, whether extruded or expanded, as much as we can. It has zero thermal mass, it burns and often with a lot of black smoke, it turns into chemical waste.
Instead we use Rockwool, cellulose, sometimes wood fibre (not tested in the video above). But the poly-stuff we avoid.